A step up at $100 from your HD238?:
Alessandrio MS-1i. $109, but I think that extra 9 dollars will go a long way.
That signature fun Grado energy sound made slightly less harsh and a little more neutral. Great, detailed bass with excellent attack and body but may not extend as much as you would like. But would definitely extend better than the HD238s. Treble is non-fatiguing and has excellent articulation but can sometimes sound raspy on certain tracks. Much less harsh than an sr-80i while staying quite detailed with decent extension. Mids seemed to have stayed the same, but I find them slightly more forward than the sr-80is.
However, it isn't comfortable for more than 2 hours of usage and burn-in definately gives an improved sound (it arrived to me with cookie-cutter gritty, raspy highs, less bass and dampened feeling of midrange).
Another suggestion is:
HD555s with the 555 to 595 foam sticker removal mod. $95, that great relaxing Sennheiser house sound with quite forward mids, laidback highs and smooth texture bass.
It would be my second recommendation just because they are so comfortable for long periods of usage (8hrs+) even with its somewhat high clamping force and gives a great soundstage with excellent separation and some of the best mids for under $100. However, the bass can be weak, slow, and flabby but remains with good, smooth, non-fatiguing texture. Overall detail of the sound signature, however, is lacking as compared to that of the Alessandro MS1is.
Another suggestion is:
AD700s for its 6 hour cuddly pillow-like comfort (short term more comfortable than HD555s but because the earpads slightly push on ears, ears get sore after 6 hours) and the best highs you can get for under $100.
This is a very easily described sound: mid-high centric. Great extension for under $100 with excellent detail. Bass is detailed but lacks in quantity. Mids seem just slightly recessed but mid-highs are more forward and overall it is a great sounding headphone if you are into highs. The soundstage is absolutely enormous, however the separation is mediocre.
Note that I own the ATH M50s and I don't like them. I only use them for monitoring purposes, paired with my HD280s. The mids feel too recessed and vocals that fall in the mid-high range sound extremely fatiguing and raspy because of its harsh highs. Do note that I have burned them in. The only part I enjoy for these headphones are its great, detailed, punchy, tight, well-extending, and full bodied bass. Probably the best bass for the price range (although it falls more into the $130 range).